This invention relates to a printer and, more particularly, to a printer for printing an image on a recording medium by using a line-type printhead.
A printhead mounted in a conventional ink-jet printer has a considerably smaller print width than printing paper. The printhead is therefore mounted in the printer to oppose printing paper, and a carriage on which the printhead is mounted is laterally moved to perform a serial print operation.
Density unevenness of a printed image in such a printhead is corrected by, for example, controlling the print operation of the printer by a reciprocal printing method.
As an effective printing method for a printhead mounted in a conventional ink-jet type printer, a double pulse control printing method is known. In this method, a short pulse is applied to each nozzle heater of the printhead first, and a long pulse is then applied to each nozzle heater.
In a line printer incorporating a full-line printhead having the same print width as that of printing paper, since the print width is large and the number of nozzles for discharging an ink is large, variations in ink discharge amount per orifice and the discharge direction cannot be neglected, unlike those in a printhead mounted in a serial printer like the above conventional printer. In addition, the line printer cannot employ the reciprocal printing method, which can be employed by the serial printer, owing to its structure.
Under the circumstances, a print control method different from that employed by the serial printer is required for the line printer to obtain a high-quality printed image free from density unevenness by making the ink discharge amounts from the ink discharge nozzles uniform.
Furthermore, in the line printer incorporating the full-line printhead described above, since a large number of nozzle heaters are also used, due to uneven energization of the nozzle heaters depending on the printing density, and changes in operating temperature, the internal temperature of the printhead cannot be kept constant for a proper print operation, resulting in variations in the ink discharge amounts from the respective nozzles. For this reason, it is difficult to maintain good print quality.
In the printer having the full-line printhead with the same print width as that of printing paper, since the structure of the printhead is different from that of a printhead having a small print width, printhead control is required in consideration of the following points to maintain high print quality:
(1) Since the nozzle heaters used for the ink discharge nozzles of the full-line printhead are driven by a plurality of LSIs, variations in ink discharge amount must be suppressed in units of LSIs in consideration of variations in the quality of LSIs.
(2) Control must be performed to suppress variations in ink discharge amount due to a temperature gradient in the printhead which is derived from a long print width.
(3) Control must be performed so as not to damage the nozzle heaters when large currents are supplied to the nozzle heaters to perform control operations (1) and (2).